Suspensions for suspending sliders in hard disk drives are well known in the art. Referring to FIG. 1, in a typical hard disk drive, the disk drive's read-write transducer 10 is included in, or mounted to, a slider 12. The slider has an aerodynamic design and is supported by a suspension 14. The slider's aerodynamic design allows for airflow between the slider and the disk drive's spinning disk 16. This airflow generates lift, which allows the read-write transducer to fly above the spinning disk's surface 18 at an optimal distance for reading data from, or writing data to, the disk.
Referring additionally to FIG. 2, which is a simplified partial side elevational view of the slider and a distal end 20 of the suspension 14, a typical suspension includes a gimbal 22 at the suspension's distal end, and a load beam 24. The gimbal typically is bonded to the load beam by laser welding or adhesive bonding. Typically, the load beam is formed from stainless steel (“SST”) foil and includes a spring portion 30 that applies a loading force, also known as a “pre-load” or “gram force,” to the slider 12. The pre-load force counteracts the lift that is generated by the airflow between the slider and the spinning disk 16, and brings the slider into a predetermined close spacing to the disk surface 18 while the disk is spinning. A proximal end 32 of the load beam is coupled to a baseplate and subsequently an actuator arm 34. The actuator arm moves under motor control to precisely position the slider, and thus, the disk drive's read-write transducer 10 relative to the disk surface.
As shown in FIG. 2, the gimbal 22 supports the slider 12. In particular, a top surface 36 of the slider is coupled to a tongue-shaped part (also referred to as a “tongue”) 38 of the gimbal, for example, using an adhesive bond. The distal end 40 of the load beam 24 includes a hemispherical projection (also referred to as a “dimple”) 42 against which the tongue of the gimbal rests after the gimbal is connected to the load beam. The gimbal, in combination with the load beam's dimple, allows the slider to pitch and roll in response to changes in airflow between the slider and the disk drive's spinning disk 16 that result from irregularities in the disk's surface 18, and to changes in the velocity of the air that is induced by the spinning disk, typically referred to as windage.
Referring additionally to FIGS. 3, 4, and 5, the gimbal 22 includes two struts (also known as “outrigger struts”) 44 and 46 that couple the gimbal's tongue 38 to the gimbal's proximal end 48, which, in turn, couples to the load beam 24. The strut includes the following three layers: a supporting layer 50, a conducting layer 52, and an insulating layer 54, which is coupled between the supporting layer and the conducting layer. The combination of the conducting layer, the insulating layer, and the supporting layer form a microstrip transmission line configuration. FIG. 5 illustrates the fact that the height of the conducting layer (“HCL”), the height of the insulating layer (“HIL”), and the height of the supporting layer (“HSL”) remain constant along the length of the strut.
The supporting layer 50 is configured to provide mechanical support for the insulating layer 54 and the conducting layer 52. Typically, the supporting layer is made of a supporting material, e.g., stainless steel (“SST”), the insulating layer (also referred to as a “dielectric layer”) is made of an insulating material, e.g., polyimide, and the conducting layer is made of a conducting material, e.g., copper or an alloy thereof. The conducting material is formed into traces 56 that are configured to be coupled to electrical leads (not shown), which interface with the slider's read-write transducer 10. An overlay layer 58, e.g., a low-temperature, modified, acrylic insulation film or a photosensitive resin, can cover the conducting layer, electrically insulating the conducting layer's traces from one another, and inhibiting corrosion of the conducting material. As shown in FIGS. 4 and 5, the overlay layer has a height (“HOL”), which when combined with the height of the conducting (“HCL”), the height of the insulating layer (“HIL”), and the height of the supporting layer (“HSL”) equal the height of the strut (“HS”).
If the conducting layer 52 is made of a copper alloy, the conducting layer typically is formed by cold rolling, which is a process that is known to individuals having ordinary skill in the art. After the conducting layer is cold rolled onto the insulating layer 54, the conducting layer is processed to form traces 56 by subtractive chemical milling, e.g., chemical etching. An increasingly popular method for manufacturing conducting layers formed from pure copper is through additive manufacturing methods, e.g., circuit integrated suspension (“CIS”) technology or Additive Circuit Gimbal (“ACG”) technology, in which the conducting layer traces are created by depositing, e.g., plating or electrodepositing, pure copper onto the insulating layer. ACG technology provides some advantages over traditional manufacturing methods, e.g., cold rolling copper alloy, in terms of the capability to generate smaller spacing between traces, which results in a smaller pitch, i.e., the distance between the centers of adjacent traces, and offers higher resolution and improved design density and functionality. Pure copper is considered by individuals having ordinary skill in the art to be greater than or equal to 99.5% copper.
Typically, the gimbal 22 is secured to the load beam 24 by spot welding the proximal end 48 of the gimbal to the load beam's bottom surface 60. After welding the gimbal to the load beam, the gimbal has to satisfy various mechanical requirements (also referred to as “mechanical characteristics”) such as stiffness and geometrical requirements in terms of angles (pitch and roll angles for different axes of rotation). The main factor that influences the mechanical requirements of the gimbal is the supporting material, followed by the conducting material. In comparison to the supporting material and the conducting material, the insulating material has very little influence on the mechanical requirements of the gimbal. The geometric requirements, e.g., the pitch and roll angles, are met by adjusting the gimbal at specified locations through either mechanical processes, which are discussed below, or laser adjust processes, both of which are known to individuals having ordinary skill in the art (See the following U.S. patents, which are incorporated by reference herein: U.S. Pat. No. 5,588,200 to Schudel, and U.S. Pat. No. 6,697,228 to Mei et al.).
During operation of the disk drive, the gimbal's tongue 38 supports the slider 12 in a spaced relation to the disk surface 18. It is desirable for the slider to be oriented roughly parallel to the surface of the spinning disk 16, even if the slider is in an unloaded position, i.e., the slider has been pulled away from the surface of the disk and is no longer flying above the spinning disk. If the slider is not oriented roughly parallel to the disk surface, the slider may contact the surface of the disk when the slider is loaded into its flying position. As improvements are made in computer disk drive technology, disk drive sliders are being designed to fly closer to disk surfaces, and thus, the relative orientation of sliders to the disk surfaces becomes even more critical.
A slider's 12 orientation relative to the disk surface 18 is dependent upon the pitch static attitude (“PSA”) of the suspension 14. To ensure proper orientation, a suspension, or a portion of the suspension, e.g., the gimbal 22, is adjusted during manufacturing so that the gimbal's tongue 38 is approximately parallel to the expected plane of the disk surface. This adjustment, which is referred to as the pitch static attitude adjustment (“PSA adjustment”), is required when the PSA of the suspension after the connection of the gimbal to the load beam 24 is different from a target value.
In general, a PSA adjustment of a gimbal 22 includes bending and/or twisting the gimbal to bring the gimbal's tongue 38 into the desired orientation. More specifically, adjustment of the suspension's final PSA is accomplished by micro-bending the suspension assembly 14 including the gimbal. For example, the PSA adjustment of a gimbal can be facilitated by attaching a pair of clamps to each strut 44 and 46 of the gimbal, and using the clamps to move, e.g., bend and/or twist, the gimbal so the tongue is brought into the desired orientation relative to the expected plane of the disk surface 18. If a PSA adjustment is not performed on the gimbal, the gimbal's tongue may not be oriented parallel to the disk surface, and there is a higher likelihood that an edge 62 or corner 64 of the slider 12 will contact and damage the disk surface. More precise thermal adjustment methods using lasers and other infrared (“IR”) sources to micro-bend materials have been developed, as discussed in U.S. Pat. No. 5,228,324 to Frackiewicz et al. and U.S. Pat. No. 5,588,200 to Schudel, which are incorporated by reference herein. Current volume production product posses a greater than 1.5 cpk at +/−0.35° PSA for both pitch and roll characteristics.
One observation that is related to the transition from subtractive processes, which use a copper alloy, to additive processes, which use pure copper, is that the shape of the suspension 14 after the PSA adjustment process slowly reverts to its original configuration, i.e., the suspension's shape prior to the PSA adjustment process, due to the inherent creep in the pure copper. The copper that is used in the additive processes has significantly lower creep resistance in comparison to the harder, stronger copper alloy that is used in the subtractive processes. The copper alloy has a higher resistance to creep because of its composition. The lower creep resistance of pure copper leads to longer settling times after the suspension is formed. This happens because the soft pure copper creeps for many hours or days after the bending that is performed as part of the PSA adjustment process, and before the copper reaches its new equilibrium state.
The longer settling time for pure copper leads to manufacturing throughput issues and larger variations in the final adjusted roll static attitude (“RSA”), pitch static attitude (“PSA”), and gram load values. The creep resistance of a material is proportional to the tensile strength of the material. The yield strength of plated pure copper after normal additive circuit processing is 90-100 MPa, which is significantly less than the yield strength (greater than 500 MPa) of the alloy copper that is used in subtractive processes.
It should, therefore, be appreciated that there is a need for a disk drive suspension 14 that includes a gimbal 22 having a plated or electrodeposited conducting layer 52 with minimal creep. The present invention satisfies these needs.